1. Field of the Invention
The present invention relates to a data transfer method of a magnetic recording/reproducing apparatus which transfers data from a host computer and so on, and records the data by a magnetic recording/reproducing apparatus, or reproduces data by the magnetic recording/reproducing apparatus and transfers the data to the host computer and so on, and more particularly to a data transfer method capable of minimizing the stop time of the magnetic recording/reproducing apparatus or the waiting time of the host computer and so on even if the data transfer density varies.
2. Description Of the Related Art
Large-capacity memory devices, such as a hard disk device, have been popularized with the increase of the amount of data to be handled by computers. Such a kind of memory device needs a large-capacity recording medium for backup. Accordingly, there has been developed a magnetic recording/reproducing apparatus for achieving large-capacity data backup by using a magnetic tape substantially equivalent to a magnetic tape for a digital audio tape recorder (DAT).
When the recording/reproducing apparatus is used, for example, in the case of a recording operation, data transferred from a hard disk device built in or connected to a host computer 1 is stored in a buffer memory in a control device of a magnetic recording/reproducing apparatus 2 as shown in FIG. 5, recording data in a predetermined format is created based on the data recorded in the buffer memory, and recorded on a magnetic tape by a rotary head. In a normal constant speed mode of a magnetic recording/reproducing apparatus using a magnetic tape for a DAT, the number of revolutions of a rotary head having a diameter of 30 mm is 2000 rpm and the feeding speed of the magnetic tape is 8.15 mm/s.
The transfer speed of data reproduced from the hard disk device and transferred from the host computer does not always agree with the data recording speed in the aforementioned constant speed mode of the magnetic recording/reproducing apparatus of the rotary head type. Furthermore, it is assumed that the data transfer is intermittent and that the data transfer density-is not constant. FIG. 6(A) illustrates the density and transfer time of data transferred from the host computer 1 with respect to the time axis. The data transfer density is divided into three levels, high density, medium density and low density as shown in patterns (a), (b) and (c), respectively.
As shown in FIG. 6(A), if the rotary head has a diameter of 30 mm, data which is transferred from the host computer 1 intermittently and in different transfer densities, are conventionally recorded in a constant speed mode in which the number of revolutions of the rotary head is 2000 rpm and the feeding speed of the magnetic tape is 8.15 mm/s. Therefore, it is necessary to perform recording only while the transferred data is stored in a buffer memory and sent out to the mechanism portion of the magnetic recording/reproducing apparatus, and to stop the operation of the mechanism portion when the data in the buffer memory runs out. The recording operation in the constant speed mode is therefore intermittent as shown in FIG. 6(B). Thus, the magnetic recording/reproducing apparatus repeatedly stops and starts up. The number of repetitions is almost the same as the number of transfer times of data from the host computer.
Such repetition of start and stop of the magnetic recording/reproducing apparatus hastens the wear and fatigue of the mechanism. Furthermore, in the case of an actual magnetic recording/reproducing apparatus, since the approach run of the magnetic tape and the search for the record leading end of the magnetic tape are needed when the apparatus is restarted after it is stopped, the control of the mechanism is complicated. When such operations are repeated, the damage to the magnetic tape as well as the fatigue of the mechanism is accumulated.
This problem also arises in the case where data is reproduced from the magnetic recording/reproducing apparatus and transferred from the host computer to a hard disk device or the like. In other words, the data receiving speed of the host computer does not always agree with the data reproducing speed of the magnetic recording/reproducing apparatus. In this case, when the data receiving operation in the host computer is stopped, it is necessary to stop the magnetic recording/reproducing apparatus at the time where the data amount in the buffer memory of the apparatus is increased to a maximum. In the case where the process speed is high as in recent computers, the reproducing speed of the magnetic recording/reproducing apparatus cannot come up with the receiving speed of the host computer. Therefore, it is sometimes required to make the receiving of the host computer on standby.
In order to solve the above problem arising from the repetition of start and stop of the magnetic recording/reproducing apparatus, for example, the recording operation of the magnetic recording/reproducing apparatus is not stopped when the data shown in FIG. 6(A) is intermittently transferred, and dummy data is recorded on a magnetic tape while the recording operation shown in FIG. 6(B) is stopped. This method makes it unnecessary to repeat the stop and start of the magnetic recording/reproducing apparatus, and enables a continuous recording operation. However, the memory capacity of the data on the magnetic tape is reduced by the amount of the dummy data. Furthermore, the recording area of the dummy data is uselessly read in reproduction, and thus the operational efficiency is lowered.